1. Field of the Invention
The present invention relates to a method of polymerizing vinyl chloride monomers or vinyl chloride monomers and monomers copolymerizable with the vinyl chloride monomers (to be referred to as "vinyl chloride series monomers" or simply "vinyl chloride", hereinafter).
2. Related Art Statement
In polymerizing vinyl chloride series monomers, the reaction speed is rapidly increased at the later period of the polymerization. Namely, an autocatalytic behavior is seen. At this period a marked exothermic heat is occurred, so that a cooling ability of an apparatus used for the polymerization must be designed maximum to meet or compensate the maximum of the exothermic heat. As a result, the cooling device of the apparatus has to be operated with a far lower cooling than the maximum cooling ability before the maximum of the exothermic heat. Hence, in order to utilize the cooling ability of the apparatus maximum, a so-called isokinetic polymerization which exhibits a stable exothermic heat from the initial to the later period of the polymerization, has been heretofore desired.
For that purpose, a means has been adopted of uniforming the polymerization reaction speed by co-using a fast polymerization initiator which exhibits a large reaction speed at the initiation period of the reaction and a retarded polymerization initiator which exhibits a large reaction speed at the later period of the reaction.
In such a case, as the retarded polymerization initiator, use is made of conventional polymerization initiator of which a temperature of a half life of 10 hours in a 0.1 mol solution thereof in benzene (to be referred to as "half life temperature at 10 hours" or "T1/2(1 H)", hereinafter) becomes within a range of 40.degree.-65.degree. C. Illustrative examples thereof are t-butyl peroxy neodecanoate (abbreviated as "BND", hereinafter), 3,5,5-trimethyl hexanoyl peroxide (abbreviated as "INPO", hereinafter), bis(2-ethyl hexyl)peroxydicarbonate (abbreviated as "OPP", hereinafter), and the like.
As the fast polymerization initiator, development and use is made of polymerization initiator of which T1/2(10H) becomes 40.degree. C. or less. Illustrative examples thereof are acetyl cyclohexyl sulfonyl peroxide (abbreviated as "ACSP", hereinafter), cumyl peroxy neodecanoate (abbreviated as "CND", hereinafter), 1,1,3,3-tetramethylbutyl peroxy neodecanoate (abbreviated as "OND", hereinafter), and the like.
Isokinetic polymerization has been possible by combining the above fast polymerization initiator and the retarded polymerization initiator and adjusting the mixing ratio and the use amounts thereof. However, physical properties of obtained polymers are not always satisfactory. For example, ACSP has drawbacks of producing an unsanitary decomposition product and a thermally unstable polymer (colored during the polymerization). CND produces a polymer having a peculiar odor because of its decomposition product. OND is inferior to ACSP and CND in polymerization activity, so that it has less effect as the fast polymerization initiator, though it has no trouble with regard to physical properties of the obtained polymer.